Lowering the temperature of the squid giant synapse prevents EPSP initiation of the postsynaptic action potential and permits investigation of the relationship between the EPSP and the presynaptic action potential. This study revealed that transmitter release is temperature sensitive; from an Arrhenuis plot, an apparent activation energy of 74 kcalorie per degree, was calculated. A change in presynaptic spike height does not appear to be the major factor involved in the sensitivity of transmitter release to temperature. BIBLIOGRAPHIC REFERENCE: Weight, F.F. and Erulkar, S.D.: Synaptic transmission and effects of temperature at the squid giant synapse. Nature 261: 720-722, 1976.